1. Field of the Invention
The present invention relates to an engine for an outboard engine system comprising a cylinder head coupled to a cylinder block by a plurality of first coupling bolts disposed at substantially equal distances from a cylinder axis so as to surround an outer periphery of a cylinder, and a cooling water passage having an opening which is defined in a cylinder head/cylinder block coupling surface at a location radially outside the first coupling bolts as viewed from the cylinder axis.
2. Description of the Related Art
An engine for an outboard engine system is disclosed in Japanese Patent Application Laid-open No. 3-31094, in which an exhaust passage is vertically defined on one side of a cylinder block in which a crankshaft is vertically supported. If the exhaust passage is vertically defined on one side of a cylinder block in the above manner, an exhaust gas from the engine mounted at an upper portion of the outboard engine system can be easily guided into an exhaust gas expanding chamber within an extension case mounted at a lower portion of the outboard engine system.
If cylinder bores are enlarged with an increase in size of the engine for the outboard engine system, the fastening force of the surface coupling both the members may be weakened, resulting in a reduced sealability, in some cases, unless the number of bolts for coupling the cylinder head to the cylinder block is increased and/or the diameter of the bolts is increased.